Analysis of molecular changes triggered by the phytohormone indole-3-acetic acid (IAA)

To elucidate the physiological changes induced by IAA treatment in Escherichia coli K-12, we used DNA micro- and macro-arrays, two-dimensional gel electrophoresis and other biochemical techniques. By micro-array analysis we found that 67 genes showed altered expression level in IAA-treated cells. About one third of these genes encode cell envelope components or proteins involved in bacterial adaptation to changes in environmental conditions. A similar amount of genes are involved in tricarboxylic acid cycle (TCA), glyoxylate shunt and amino acid biosynthesis. Furthermore, we investigate the effect of IAA-treatment on some structural cellular component that may be involved in cellular response to stress and found an increased production of lipopolysaccharide (LPS), exopolysaccharide (EPS) and biofilm. This effect correlates with an increase of the DnaK chaperone concentration. To confirm the indications obtained from the macroarray analysis we measured the activity of 35 enzymes involved in the central metabolism and evaluated the level of 5 metabolites. We found that the enhanced production of acetyl-CoA and the decrease of NADH/NAD+ ratio are connected with the IAA-response. IAA treated cells survive more than untreated cells. Our results suggest that IAA-treatment is a stimulus capable of inducing changes in bacterial gene expression leading to the activation of cellular protection systems and to the induction of the central metabolic pathways in E. coli.